Ok so now I have created an app that I want to sell on Google play. As I have never published anything there before it seems to be a good idea to post my question in this forum to help myself and others who follow in the same footsteps. Do I have to use the Google in-app API library to publish my app on Google play or is it just to simplify for users when running the app for example do I need to create two APK files and use the in-app API in the trialversion app with a "upgrade to fullversion" button to allow the user to purchase the full version of the app? Or is it just to upload one version with an inbuildt password that unlocks the app. Then I assume that Google play purchase must provide the password to be able to unlock all features. I have read Googles wiki for their marketplace and I think only one APK is allowed which means passwords must be build in? Thanks for all posts that may be of help. I can perhaps make it simple for myself to upload the version that cost money but it would be more effective to allow users to try a trialversion and decide if they want to unlock features in the app. Thanks